1. Field of the Invention
The present invention relates to a golf ball, and more particularly to a solid golf ball having an improved shot feeling, resilience on shot and controllability.
2. Description of the Prior Art
Heretofore, balata rubber (natural rubber or synthetic transpolyisoprene rubber) or a mixture of balata rubber and elastomer has been used as a material for covers of so-called high-class golf balls. It is easier to put spin to golf balls having covers made of balata rubber because balata rubber is relatively soft and provides the golf balls with good controllability. Therefore, not only professional golfers but also non-professional but advanced golfers prefer the above type of golf balls. Since durability of balata rubber is rather small, the golf ball having the cover made of balata rubber has suffered from a problem that the golf ball may be broken or damaged when the golfer failed to hit the ball at a proper portion of the ball. Thus, it is highly likely that such a golf ball has a relatively short lifetime.
Recently, there has been widely used an ionomer which is a copolymer of .alpha., .beta.-unsaturated carboxylic acid and olefin as a material for a cover of a golf ball. Ionomer is superior to balata rubber in terms of durability and flight performance. However, the golf balls with the covers made of such ionomer have suffered from another problem that golfers have a difficulty in putting spin to the balls due to the hardness of ionomer, thus lowering controllability of the golf balls. Also, the hardness of ionomer leads to a poor shot feeling.
In order to improve controllability of the golf ball, Japanese Unexamined Patent Publication Nos. 1-308577 and 5-3931 disclose the idea of using ionomer mixture composed of a hard-type ionomer and a soft-type ionomer. This idea is effective in improving controllability and shot feeling of the golf ball but lowers resilience of the cover because the hardness of the cover decreases as a whole. Consequently, the resilience of the golf ball deteriorates, and the flying distance is lowered.
There has been proposed an idea of reducing the hardness of a core of the ball as well as the idea of reducing the hardness of the cover of the ball in order to improve the shot feeling. However, deterioration of the resilience of the ball as a whole is unavoidable also in the case where the hardness of the core is reduced for the same reason as applied above in the case where the hardness of the cover is reduced.
Also, there have been proposed various techniques of adding a variety of compounds as a material for the core to improve the resilience of the core, as disclosed in, for example, Japanese Examined Patent Publication Nos. 3-1335, 3-1336, 3-1337; and Japanese Unexamined Patent Publication Nos. 2-297384, 4-109970, 8-98901. None of them has proven to be effective in improving the resilience of the core of the ball.
As mentioned above, there has not been known a golf ball with a cover composed of ionomer which attains an improvement in shot feeling, controllability and resilience.